In the process of monitoring the voltage signals, it is usually needed to detect whether the relative voltage difference value between two voltage signals meets a certain requirement, for example, when the input signal A is 100 mV greater than the input signal B, it could allow to output a logic level signal. In order to realize the function, the comparator circuit is required to use; while the traditional comparator structures are mostly the grid-input, which can only realize the equivalence detection, and the detection of the relative difference value must be realized through the method of increasing the detuning or delaying; while the circuit precision increased by that type of structure will be changed along with the change of the device Corner (process deviation), and especially when the required difference value is less than 100 mV, the change of the Corner may be greater than the required difference value, which is difficult to meet the requirement for batch production; in addition the gate-source device bearing the high voltage is required to be used while the input signal is a high voltage field, and that type of device needs the extra process layer which will increase the process cost; while if the process layer is not added, it will limit the range of the input signal. So, the structure of the traditional grid input is limited by the precision, which can only be applied to the scene of which the requirement to the precision is not high, and is limited by the process cost, which can only be applied to the scene that the input signal is the low voltage field.